This application is related to Japanese application No. 2002-023772 filed on Jan. 31, 2002, whose priority is claimed under 35 USC xc2xa7 119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a semiconductor device and a fabrication method therefor. More specifically, the invention relates to a semiconductor device having a condenser lens for use in a solid image-pickup device such as a CCD (charge coupled device), a liquid crystal display device and the like, and to a fabrication method therefor.
2. Description of the Related Art
Solid image-pickup devices such as CCDs and MOS (metal oxide semiconductor) image-pickup devices are employed for various applications, e.g., digital cameras, video cameras, cellular phones having cameras, scanners, digital copying machines and facsimile machines. As these products come into widespread use, demands for higher functions (increase in pixel number and improvement of photosensitivity), size reduction and cost reduction of the solid image-pickup device are correspondingly increased. For the size reduction and pixel number increase of the solid image-pickup device, the size of each pixel incorporated in the solid image-pickup device is further reduced. As a result, the photosensitivity of the solid image-pickup device (which is one of fundamental performance requirements) is reduced, making it difficult to pick up a clear image under a predetermined illuminance.
A known approach to this problem is to provide a micro-lens of an organic polymeric material on a color filter for improvement of the photosensitivity (see, for example, Japanese Unexamined Patent Publication No. HEI4-12568 (1992)). Another approach is to employ a condenser lens (so-called intra-layer lens) provided in a laminate structure between a light receiving portion and a color filter in combination with the aforesaid micro-lens for improvement of the photosensitivity (see, for example, Japanese Unexamined Patent Publication No. HEI11-40787 (1999)).
A fabrication method for a conventional CCD solid image-pickup device having an intra-layer lens will hereinafter be described with reference to FIGS. 2(a) to 2(e). A unit cell of the conventional CCD solid image-pickup device fabricated by the fabrication method shown in FIGS. 2(a) to 2(e) is illustrated in section in FIG. 1.
As shown in FIG. 2(a), a light receiving portion 2, a reading gate portion 3, CCD transfer channels (transfer portions) 4 and a channel stopper 5 are formed in a semiconductor substrate 1 by implanting desired impurity ions into the semiconductor substrate 1. In turn, transfer electrodes 7 having a predetermined pattern are formed on the surface of the semiconductor substrate 1 with the intervention of an insulating film 6, and a light shielding film 9 is formed as covering the transfer electrodes 7 with the intervention of an inter-level insulating film 8. Then, the light shielding film 9 is patterned so that an opening is formed therein above the light receiving portion 2.
As shown in FIG. 2(b), an overcoat layer 10 is formed on the light shielding film 9 for planarization of the surface. The overcoat layer 10 is, for example, a BPSG (boro-phospho silicate glass) film formed by a reflow process.
As shown in FIG. 2(c), an intra-layer lens material layer 16 having a high refractive index for formation of an intra-layer lens 11 (see FIG. 1) is formed on the overcoat layer 10. The intra-layer lens material layer 16 is, for example, a silicon nitride film formed by a plasma CVD process.
As shown in FIG. 2(d), a resist 17 is applied on the intra-layer lens material layer 16, then patterned, and re-flowed at about 160xc2x0 C. so as to be formed into a lens shape.
As shown in FIG. 2(e), the intra-lens material layer 16 is dry-etched to be shaped into the intra-layer lens 11 by copying the lens shape of the resist 17 to the lens material layer 16.
Thereafter, a transparent film 12 having a low refractive index is formed over the intra-layer lens 11 and planarized for increasing the light convergence ratio of the intra-layer lens 11. Then, a color filter 13, a protective film 14 and a micro-lens 15 are sequentially formed on the transparent film 12. Thus, the CCD solid image-pickup device 18 shown in FIG. 1 is provided.
However, the aforesaid conventional fabrication method, in which the transparent film having a low refractive index is formed on the intra-layer lens and the color filter is directly formed on the transparent film, has the following drawbacks. In order to allow the intra-layer lens to provide a desired lens effect, an organic polymeric material generally employed as a material for the transparent film is required to have a low refractive index.
A known method for reducing the refractive index of the transparent film is to employ an organic polymeric material containing a greater amount of fluorine (see, for example, Polymer Vol. 34, March 1995). However, such a fluorine-containing material is highly water-repellent and oil-repellent and, hence, has poor adhesion to other materials. Where a dye-absorptive resist (e.g., casein or gelatin), a color resist or a resist for micro-lens formation is applied on the surface of the transparent film of the fluorine-containing material, for example, the resulting color resist layer or micro-lens layer is liable to have an uneven geometry because even application of the resist is difficult.
More specifically, there is a possibility that the color filter 13 formed by the aforesaid conventional method has an uneven thickness and is separated from the transparent film. Particularly in the case of the solid image-pickup device, this results in a poorer image quality and deterioration in product yield and product quality.
A conceivable method for improvement of the adhesion of the transparent film to the other materials is to perform an oxygen plasma treatment on the surface of the transparent film in an oxygen-containing atmosphere. However, the oxygen plasma treatment alone is insufficient for the improvement of the adhesion.
In view of the foregoing, the present invention is directed to a semiconductor device and a fabrication method therefor which ensure improved adhesion between a transparent film and an optical element such as a color filter or a micro-lens provided on the transparent film and are free from deterioration in product yield and product quality.
According to the present invention, there is provided a semiconductor device comprising: a semiconductor substrate having a light receiving or emitting element; a condenser lens provided above the element; a first transparent film provided on the condenser lens for planarization over the condenser lens; a light-transmittable optical element provided above the first transparent film; and a second transparent film interposed between the first transparent film and the optical element; wherein the first transparent film is comprised of a fluorine compound so that the first transparent film is lower in refractive index than the condenser lens and the second transparent film is lower in water- and oil-repellent properties than the first transparent film.
Since the second transparent film having the lower water- and oil-repellent properties than that of the first transparent film is interposed between the first transparent film and the optical element in the inventive semiconductor device, the optical element can be combined with the first transparent film with improved adhesion.